Add demo with ANNs

Squashed commit of the following:
commit 37b8710bf418efc954287accc616437c440de941
Author: Alexander Fabisch <afabisch@tzi.de>
Date:   Sat Aug 31 23:45:00 2013 +0200

    Add comment

commit 9718f404c432ec374be8220dbd2092042cee9d2c
Author: Alexander Fabisch <afabisch@tzi.de>
Date:   Sat Aug 31 23:41:37 2013 +0200

    Relax type requirements

commit 33175da3cef20da3c503e35de51c80fc5c8443f8
Author: Alexander Fabisch <afabisch@tzi.de>
Date:   Sat Aug 31 23:34:25 2013 +0200

    Remove duplicate comments

commit 92d3c74ee143c548529c311258846d079a227e08
Author: Alexander Fabisch <afabisch@tzi.de>
Date:   Sat Aug 31 23:31:51 2013 +0200

    Add arguments to demo functions

commit acde2e9aa302309877de43d110fedb0a957c59e1
Author: Alexander Fabisch <afabisch@tzi.de>
Date:   Sat Aug 31 22:39:30 2013 +0200

    Merge evaluation of MLR and ANN

commit 2c84ab5e54ee16809e0abbc79f5a6a55e9e61cc4
Author: Alexander Fabisch <afabisch@tzi.de>
Date:   Sat Aug 31 18:02:55 2013 +0200

    Evaluate on test set

commit e9f7793470c59cf28d018e01a4c0b07392e6380a
Author: Alexander Fabisch <afabisch@tzi.de>
Date:   Sat Aug 31 17:55:52 2013 +0200

    Use generic SGD for ANN

commit a7d9778466b8791f87b2ee55c2e206c10b9b3b8a
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Sat Aug 31 09:50:48 2013 +0200

    Make SGD more generic.

commit dd0900b5e2f7b48be2c51f5f57e2169c815a814e
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Sat Aug 31 01:26:23 2013 +0200

    Add type 'MLR'

commit bcb9686bd3744d6f1a32695495eeeaf9e2af8f17
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Fri Aug 30 22:15:37 2013 +0200

    First test with MNIST and ANN.

commit 5ba0c86199efc78e378ee2b6b7d59e0a7986f919
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Fri Aug 30 09:11:09 2013 +0200

    Fix obvious errors

    Dimensions of gradients still don't really fit yet.

commit c6aba6801f41fc756d17242f6bf342565ad5fa8b
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Thu Aug 29 23:50:55 2013 +0200

    Implement first version of backprop

commit da6299edc4385716c1d2d47e321e5582862a2233
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Thu Aug 29 07:29:47 2013 +0200

    Add scaffold for backprop

commit 4a4a535a4de7e07de9be48171043e3cf92fca1a3
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Mon Aug 26 08:58:53 2013 +0200

    Forward propagation

commit 9cfda600d241448b46b95c5e6817818f2c539df9
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Sun Aug 25 22:12:32 2013 +0200

    Add getter and setter for weight matrices

commit 7a4ec339c32f3fe0c569f1b69c679bc2320557c5
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Sun Aug 25 13:57:37 2013 +0200

    Add type ANN

commit 056f6809d567a1d7c537e46398ca850e0e1623fd
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Sun Aug 25 12:45:14 2013 +0200

    Add utils.jl, make functions generic

commit dcf3d2386c7465946f4457fa04323f23efb39405
Author: Alexander Fabisch <afabisch@googlemail.com>
Date:   Sat Aug 24 21:07:23 2013 +0200

    Refactor MLR